Plasma is an ionized gas that conducts electricity, and is created by adding energy, such as electricity, to an electrically neutral gas, such as compressed air. By adding electricity through an electrode (hafnium), the gas becomes imbalanced and conducts electricity. The more electrical energy added, the hotter the plasma arc becomes. Plasma arc cutting machines control this powerful energy by constricting the arc and forcing it through a cutting torch having a nozzle. By increasing air pressure and intensifying the arc with higher voltages, the arc becomes hotter and more capable of blasting through thicker metals and blowing away the cuttings. Plasma arc cutting systems require a power source, a plasma cutting torch, compressed gas, electrical power, and a supply of tips and electrodes. Plasma arc cutting machines can rapidly and precisely cut through any electrically conductive metal without preheating and with a minimal heat-affected zone. Plasma can cut metals such as aluminum, stainless steel, brass, and copper in excess of two inches thick, along with expanded and stacked metals.
In oxy fuel cutting, an oxygen/fuel gas flame preheats the metal to its ignition temperature, and a high-power oxygen jet is directed through a cutting torch at the metal creating a chemical reaction between the oxygen and the metal to form iron oxide, also known as slag. The high-power oxygen jet removes the slag from the kerf. Cut quality, preheating times, and thicknesses can be influenced by the type of fuel gas used. Oxy fuel cutting is used for ferrous, mild and low-alloy steels in thicknesses up to three feet or more. Oxy fuel cutting systems require a fuel tank, an oxygen tank, and a cutting torch. Oxy fuel cutting allows metalworkers to cut extremely thick metals with ease.
In order to form a beveled edge when cutting, the cutting torch must be tilted from a vertical orientation normal to the surface of the material (the cutting surface) to a tilted orientation oblique to the surface of the material. For this purpose, bevel head attachments capable of tilting a cutting torch have been used. Such bevel head attachments typically mount on a carriage of the cutting machine. In a common arrangement for CNC cutting machines, the carriage is adapted for travel side-to-side along a transverse gantry, and the gantry is adapted to move along a longitudinal direction of a cutting table. The bevel head attachment allows the tilt angle of the cutting torch to be controlled as the carriage is displaced relative to the material being cut to provide a beveled edge along the cut path. The bevel head attachment also enables the torch to be rotated about a vertical axis to orient the torch as specified by the cut program.
Where the torch is an oxy fuel cutting torch, it connects to hoses for supplying oxygen, and for preheating oxygen and fuel gas. Where the torch is a plasma cutting torch, it connects to hoses for supplying plasma gas, hoses for supplying and delivering cooling water, and cables for electricity. Thus, the bevel head attachment should accommodate various types of hoses and electrical cables connected to the torch in a manner that permits the torch to be tilted and rotated smoothly, even as the hoses and cables flex and twist.
It is also desirable that the bevel head attachment be as lightweight as possible so that it may be mounted on different cutting machines and carriages having different load capacities.
Many traditional bevel head attachments have rotational limitation and/or high maintenance costs and machine down time associated with wear of electrical slip rings for transmitting signals across rotational interfaces and other component failures due to proximity to the cutting operation.
U.S. Pat. No. 6,201,207 discloses a bevel head attachment of the prior art. The bevel head attachment uses a motorized three-dimensional parallelogram linkage for tilting a torch holder in which the torch is received. The linkage as a whole is rotatable by another motor about a vertical axis. The disclosed bevel head attachment is generally satisfactory, but is not as light as desired.